(1) Field of the Invention
The present invention relates to a display device and particularly, to a display device in which a polarizing plate and a phase difference plate are combined with each other so as to improve visibility.
(2) Description of the Related Art
So far, in this kind of display device, a so-called white and black-reversible meter has been realized, by which a black character is displayed on a white dial plate in the daytime while a white character is displayed on a black dial plate at night taking the visibility into consideration. FIG. 25 is a front view illustrating a display image in the daytime of such a conventional display device. FIG. 26 is a front view illustrating a display image at night of such a conventional display device.
In this kind of display device, for example, as shown in FIG. 25, a transmission-type character and scale to be indicated by a pointer 92 are formed on a white dial plate 91 exposed from a facing 93.
In the daytime, as shown in FIG. 25, in order to let a character and scale be seen black, an outer periphery of a character and scale is hemmed in black or, alternatively, a smoke plate is entered in a transmission part. At night, since the surroundings becomes dark, as shown in FIG. 26, an illumination is not done with respect to a white dial plate so as to let the dial plate be seen black artificially while a white color illumination is transmitted through a character and scale from the back so as to let the character and scale be seen white.
An example of a conventional display device using a polarizing plate is disclosed in Japanese Utility Model Application Laid-Open No. H6-885 and Japanese Patent Application Laid-Open No. H10-301103.
However, in the daytime, when a strong outer light enters, an illumination part at the back is undesirably seen from the transmission part of the character and scale, which should primarily be seen black. For example, when a diffuser plate having a clouded color is used, the color is seen.
Further, in the twilight, when a backlight is turned on, a white color that is a background color of the dial plate is seen since the surroundings does not become really dark yet. Further, with regard to the character and scale, a white color is transmitted due to the backlight. As a result, in the twilight, the contrast between the character and scale and the dial plate is very low, causing deterioration in the visibility of the character and scale.
Moreover, at night, although the white dial plate is allowed to be seen black artificially, when an outer light enters, as shown with a reference numeral 94 in FIG. 26, a white color that is a background color of the dial plate is seen only in an area where the outer light enters, resulting in that the white character and scale becomes hard to be seen, causing deterioration in the visibility of the character and scale.